Impact of solvent sulfolane in enhancing methanol selectivity during methane partial oxidation on Fe-ZSM5 catalyst with H2O2 as an oxidant

Abstract

The liquid-phase direct partial oxidation of methane to methanol is highly desirable for methane utilization. Using a combination of density functional theory and molecular dynamics simulations, this investigation reports the impact of sulfolane solvent on the reaction mechanism of methane oxidation with H₂O₂ in Fe-ZSM-5 catalyst and the potential product distribution. Sulfolane favored the formation of [Fe–OH] and [FeO] as active oxygen species from H₂O₂ dissociation, unlike Fe-OOH in water. On [Fe–OH], methanol formation was via a methoxy intermediate (activation barrier, E_a = 1.79 eV), while on [FeO], it was by the radical rebound mechanism (E_a = 1.41 eV). The formation of formaldehyde was kinetically and thermodynamically less favorable than methanol and the formation of formic acid had a higher barrier. The lower diffusivity of H₂O₂ than CH₃OH and the lower diffusivity of these in sulfolane than in water, together with the trends in reaction barriers, indicate higher methanol selectivity in sulfolane than in water.